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- Posts: 517
- Joined: Thu Jul 14, 2016 12:08 pm
Our lab performs environmental & food analysis, and I'm in charge of developing new / optimizing current procedures / troubleshooting.
We are having some troubles with the GC-MS/MS analysis of organophosphorous pesticide residues. Basically the signal for most compounds enhances strongly in samples compared to calibration standards: the so-called matrix enhancement effect. This leads to recoveries of internal standards up to 600%.
Because the quantification is relative, internal standards compensate for this effect. But we use ~6 internal standards for ~20 analytes, and the effect is different for different types of samples. Therefore i found it impossible to quantify each batch of samples without juggling internal standards around to find the best combinations for that particular run.
I've been doing some literature research and people recommend the use of analyte protectants. I think i have a good idea on what/how much to inject with each sample but I was wondering if people here have experience with using these? And more specifically if i should be worried about the long-term effects on the system?
An external expert told me that some labs 'just add a drop of olive oil to every vial'. But I want to do this more controlled/reproducible and with minimal risk of damage to the system. What's the best way to start this safely? The injection is 25µl of hexane in PTV solvent vent mode. Is the best way to add the protectants to the vials, or let the autosampler fill the syringe with 25µl sample and then 1µl of the protectant solution?
Thanks in advance!